A solar cell module comprises a solar cell die soldered to a substrate. A known defect in the manufacturing of solar cell modules is the presence of voids in the solder between the solar cell die and the substrate. Voids in the solder can introduce at least two problems in a solar cell module. First, the solder contact area between the solar cell die and the substrate is reduced by the sum total of all void areas in the solder. The reduction in contact area increases the current density present in the solder that electrically couples the solar cell die to the substrate. Second, in concentrated photovoltaic (CPV) systems, light is focused onto a solar cell die to maximize solar energy conversion. In CPV systems, the concentration of light also concentrates substantial heat onto the solar cell die, through the die to the solder, from the solder to the substrate, and to an underlying sheet metal plane. A solder void comprises an atmosphere that reduces the thermal heat transfer area and increases the junction temperature. The increased junction temperature requires the use of heat sinks to keep the solar cell cool, otherwise the operating efficiency of the solar cell will drop significantly. The reduction in contact area further exacerbates the heating due to increased current density and can result in solar cell module failure.
To address these problems, it is preferable to control the area of any single solder void to less than 1% of the total solder area between the solar cell die and the substrate. It is further preferable to control the total area of voids to less than 5% of the total solder area between the solar cell die and the substrate.